The invention relates to a device for curing a UV-curable resin layer applied to a main surface or between two disc elements of a disc-shaped registration carrier, comprising rotation means for supporting the disc-shaped registration carrier and rotating it in a plane, and a rectilinear ultraviolet radiation source which is radially disposed with respect to the disc-shaped registration carrier for emitting ultraviolet radiation to the UV-curable resin layer, wherein the length and the position of the rectilinear ultraviolet radiation source are such that the rectilinear radiation source is disposed opposite the disc-shaped registration carrier from a distance from the centre of the disc-shaped registration carrier to the edge thereof.
A device of this kind may be considered to be known, as is indicated in passing in European patent No. 0 574 975.
In the prior art device the rectilinear ultraviolet radiation source is disposed parallel to the aforesaid plane, as a result of which the UV-curable resin layer is unevenly exposed by the ultraviolet radiation from the rectilinear ultraviolet radiation source.
The object of the present invention is to provide an even exposure of the UV-curable resin layer.
In order to accomplish that objective, the invention provides a device of the kind referred to in the introduction, which is characterized in that the rectilinear ultraviolet radiation source is disposed at an angle of between 0 and 90 degrees to the aforesaid plane.
A model has been developed on the basis of which an optimum angle can be determined, depending on the position of the rectilinear ultraviolet radiation source with respect to the aforesaid plane and the length of the rectilinear ultraviolet radiation source. This model for ultraviolet radiation energy as a function of the radius of the disc-shaped registration carrier has been verified by measurement of the unevenness in the intensity of the ultraviolet radiation over the radius of the disc-shaped registration carrier, whereby it has become apparent that this model is satisfactory in practice. It has appeared in particular that the optimum angle ranges between 20 degrees and 70 degrees, depending on the length of the rectilinear ultraviolet radiation source.
It is also possible to determine the optimum angle empirically, of course, whereby means may be provided for adjusting the said angle.
In the prior art device, additional reflectors are required for assisting in the curing of a UV-curable resin layer applied to the edge surface of the disc-shaped registration carrier. In this connection reference is also made to German patent No. 195 45 943.
Another object of the invention is to eliminate the need to use the aforesaid additional reflectors, partially because they are subject to fouling, and in order to accomplish that objective the invention provides this further aspect that the rectilinear ultraviolet radiation source is disposed opposite the disc-shaped registration carrier in such a manner that it extends beyond the edge of said disc-shaped registration carrier.
It is noted that also the device which is known from the aforesaid European patent No. 0 574 975 is capable of providing even exposure of a UV-curable resin layer applied to a main surface of a disc-shaped registration carrier whilst at the same time exposing of a UV-curable resin layer applied to the edge surface of the disc-shaped registration carrier, In this prior art device, however, a tubular ultraviolet radiation source is disposed at an angle of 90 degrees to the aforesaid plane, and a revolution body reflector is provided, on the central axis of which the tubular ultraviolet radiation source is positioned. This arrangement of the prior art device results in a low dose of ultraviolet radiation, since the larger part of the radiation is indirect radiation. In particular the portion of ultraviolet radiation that has a wavelength of less than 250 nm is too small. The reflection from the reflector is about 80% for UV-A/B and about 40% for UV-C. UV-C is important in particular for curing the UV-curable resin layer applied to the main surface of the disc-shaped registration carrier. The low dose renders it impossible to reduce the cycle time, thus necessitating the use of a tubular ultraviolet radiation source having a greater capacity, as a result of which the heat input is large.
One embodiment of the invention for increasing the light intensity is characterized in that a reflector is disposed parallel to the side of the rectilinear ultraviolet radiation source that faces away from the disc-shaped registration carrier.
In order to eliminate the phenomenon of reflector fouling, one embodiment of the invention is characterized in that the rectilinear ultraviolet radiation source is provided with a reflector on the side that faces away from the disc-shaped registration carrier. This reflector may consist of a coating which is present on part of the rectilinear ultraviolet radiation source. When this rectilinear ultraviolet radiation source is replaced, a new reflector becomes available again.
Preferably, the reflector is a cold light reflector, which transmits heat radiation.
As a result of the direct exposure in accordance with the present invention a higher ultraviolet radiation efficiency is realised, which makes it possible to use a rectilinear ultraviolet radiation source which produces deeper ultraviolet radiation, in particular up to approximately 180 nm. The present invention allows a reduction of the cycle time. Cycle times of less than two seconds are attainable.
The essence of the present invention is to provide a linear ultraviolet radiation source which is disposed at such an angle that uniform exposure will take place upon rotation of the disc-shaped registration carrier to be exposed. Since the minimum energy remains practically constant, the capacity of the rectilinear ultraviolet radiation source does not need to be higher than in the conventional case, wherein the rectilinear ultraviolet radiation source is positioned parallel to the disc-shaped registration carrier.
The UV-curable resin layer applied to a main surface of a disc-shaped registration carrier may be a protective coating, and the registration carrier of the CD-type.
The UV-curable resin layer applied between two disc elements of a disc-shaped registration carrier is a bonding, adhesive or glue layer for joining said disc elements at the time of UV-curing. The registration carrier may be of the DVD-type or SACD-type. The DVD-type registration carrier may have more than two disc elements and more than one UV-curable resin (bonding) layer (DVD 18, for instance). The UV-curable resin layer may be applied as disclosed in, for example, WO 97/36737 or DE-A1-40 41 199.